During the past decade, attempts have been made to improve the tactile or "feel" characteristics of powders and of solid compacts intended for cosmetic makeup purposes in the eye region and on the face. The general approach has been to treat the surfaces of the major pigments in these formulations. Treatment also was intended to improve the dispersion or the compatibility of the pigment in the compact formulation.
Compact formulations containing largely platy pigments or extenders such as mica already had reasonably smooth and soft tactile properties, due to the flat or platy shape of the pigment particles. However, it was recognized that these pigments could also be improved by treatment. Talc, a platy extender frequently used in compact formulations, showed several disadvantages. The softness of talc contributed to its ease of breaking up physically so that the platy character would be substantially decreased or lost. The softness of the talc also contributed to its hard compaction when subjected to pressure, so that pay-off of the formulation in use became low.
Mica, as an extender in these compact formulations, was found to overcome some of the disadvantages of the talc. Mica, as a harder material but still platy in shape, resists being broken up physically. It also has some resistance to compaction, so that by adjusting the binder formulation of the compact, a reasonably soft compact is attainable along with good pay-off.
The outer structure of human skin is a mosaic of hydrophilic and hydrophobic areas. The best tactile effects, or the best smoothness and softness, are attained with the coating of pigment surfaces with compounds that have a hydrophile-hydrophobe balance similar to human skin, and with compounds that have some chemical relationship to skin.
Mica, as well as some of the metal oxide coated mica pigments used as pearlescent and color interference type pigments in compact and powder formulations, may have more surface hydrophilic character than is desirable for good tactile qualities on the skin. This means that the surface of the mica or of the platy pigment may have some drag in being applied to the skin. The hydrophile-hydrophobe balance of the pigment surface should be shifted. This is done with appropriate treatment of the pigment surfaces. The treatment consists of coating the surfaces of the pigment with a suitable compound. In many cases, the compounds or agents used have shifted the hydrophile-hydrophobe balance very strongly toward hydrophobic. This is neither desirable nor necessary.
Compounds that have been used for pigment surface treatment include silicones, silanes, siloxanes, fatty acids, chemically modified polyolefins, and fatty acid triglycerides (fats). These generally cause a large shift towards hydrophobic character and therefore, less than desirable tactile qualities.
Others have been used that are substantial improvements over the above group. They include amino acid derivatives, lecithin, safcosine derivatives, and others based on derivatives of natural products. The hydrophile-hydrophobe shift is modest towards hydrophobic and desirable. The tactile qualities are improved. However, in some cases, rancidity may result from the oxidation of some unsaturated fatty acid components. The solubilities of some of these compounds in components of the binder formulation may be substantial, leading to removal of some of the compound from the pigment surface. Mechanical treatment in the course of preparing the formulation for compaction may result in mechanically removing some of the treatment compound from the pigment surface. Finally, the adherence or adsorption of the treatment compound to the pigment surface is questionable, so that migration of the compound away from the pigment surface may take place with time.
European Patent Publication No. 139,481 of May 2, 1985 discloses methods for treating inorganic pigments with N-mono-acylated basic amino acids containing long chain acyl groups, e.g., N.epsilon.-lauroyl-L-lysine. The publication states that any dry or wet procedure may be used. The "dry" procedure involves dry blending of the components. A "wet" procedure involves dissolving the treatment compound in an organic solvent, using calcium chloride as a solubilizing agent, bringing the inorganic pigment into contact with the solution and then washing the mixture with water to remove calcium chloride. An alternative "wet" procedure involves dissolving the treatment compound in an aqueous alkali or an aqueous solvent, bringing the inorganic pigment into contact with the solution, neutralizing the mixture, precipitating and adhering the treatment compound to the pigment surface, washing with water and drying. It is implied that the alternative methods yield equivalent products.
Of the three methods disclosed, the dry blending method is shown in Example X, infra, not to yield a satisfactory product; the only solvent mentioned in connection with a wet method is calcium ethylate, the use of which is expensive and impractical; and the alternative wet method suggested is not disclosed with sufficient particularity to enable it to be successfully practiced.
It is an object of the invention to provide an improved method for producing a treated platy pigment with improved tactile characteristics and with good adherence of the treatment material to the pigment surface. Other objects of the invention will become apparent from the following description.